Symphony Radio Fault

Hi I have a `02 Allroad 2.5Tdi with a Symphony radio, the radio will play from cold for approx 10 minutes and then loose signal, as if unplugging the antenna. It will stay in this state until the car cools down again. The length it will play for is related to how long it has been left to stand.
I have run Vag-Com but it does not show a radio fault.